Data missing may possibly occur in a file being transferred using transmission control protocol (TCP) as the transport layer communication protocol and file transfer protocol (FTP) as the application layer communication protocol. Term “data missing” in the context of this disclosure refers to the phenomenon in which only a part of a file is sent from the sending-side computer to the receiving side and the receiving-side computer recognizes the received part as the entire file. There is a method, therefore, for detecting data missing by exchanging status notification of the normal/abnormal end of file transfer between the sending and receiving sides after the file is transferred.
After receiving a file through a data transfer process, the receiving-side computer closes the received file and releases the buffer in which the received file has been stored. When receiving a status notification of an abnormal end from the sending-side computer, the receiving-side computer discards the closed file. If the status notification of the abnormal end is received before the received file is closed, the receiving-side computer may release the buffer without closing the file. Even if the sending-side computer sends a status notification upon completion of a data transfer process, the status notification of an abnormal end may occasionally be delayed and arrive at the receiving-side computer after a file closure process has completed. While the file closure process is in progress, the buffer remains allocated to store the received data. For example, Japanese Laid-open Patent Publication No. 06-301608, Japanese Laid-open Patent Publication 2000-172539 and Japanese Laid-open Patent Publication 02-157942 are issued.